Any measure of what percentage of the people using a program are abusing it can only be of the people who are known to be abusing it. Obviously they don't keep known abusers on their payroll. The entire system is a waste of money, but they don't make a point to waste as much money as possible. 

Welfare fundamentally should not be necessary. If there is a surplus of labour in one area of the country, the unemployed in that area should move to where there is work. If one industry is downsizing, the people working in that industry should seek employment elsewhere until the industry recovers. The problem with this is the simple reality that numerous people living on social assistance simply do not want off of it, and do not want to have to work for a living.